This invention relates to printing or duplicating and more particularly to dual printing in which a copy sheet is acted upon by each of two printing heads. Examples of this type of equipment are duplicators such as the Multilith Model 2675 manufactured by Addressograph Multigraph Corporation. This particular machine is a lithographic duplicator which serves both in offices and in print shops wherever dual printing is required. Such machines are capable of printing copy sheets with two impressions on the same face, such as two impressions in different colors, or of printing upon both faces of a single copy sheet by providing a turnover mechanism between the dual print heads. Each print head is equipped with automatic master insertion and ejection in keeping with known mechanical arrangements. Equipment of this sort is well-known and has long been in effective use.
With the increase in the use of duplicators in office systems where many runs of short duration are required, some duplicators have been developed which take masters one at a time from a stacked supply or from a master maker, and automatically attach each one in turn to the master cylinder, print the necessary copies, and eject the master, repeating this process with each new master.
Up until the time when this invention was made, no very practical means for handling the automation of master supply to dual systems had been discovered, because of the inherent complexities and expense related to mechanism for supplying the two print heads with masters, and to the problems inherent in trying to insure that each head would receive a master correctly related to the master simultaneously being supplied to the other head.
Printing operations with two impressions per sheet have, accordingly been normally confined to rather extended runs in which the time required for operator installation and removal of masters from the two master cylinders was not a significant factor in the overall operation. It is, however, becoming more and more important for many reasons, including economic and ecological, to make dual impressions, usually one on each face of the sheet (known as duplexing), and this is also true with respect to short, systems type, duplicating runs. Under the latter circumstances, the time and attention which the operator must devote to the proper selection, attachment and removal of masters becomes a very high fraction of the total run time, is extremely burdensome for the operator, and take his attention from equally important activities related to the overall duplicating process.
According to certain existing systems, automatic feeding of masters to each of the two print heads and discharge therefrom is arranged for, but this still involves very significant operator control because the masters must be so stacked and coordinated at the separate heads that each one will be properly related to its associated master in the other stack to insure printing on the same copy sheet. If errors in this regard should occur, the operator would not have any ready way of detecting this fact, and the result could be very costly in time and material. These systems, furthermore, do not permit automatic imaging of masters from a given set of original documents and automatic feeding of such masters to the print heads, both of which characteristics are provided in this invention.